The present invention relates to a cell flow diverter for use on spacers of a boiling water nuclear reactor for channeling flow through the spacer cells into a vortex generator or about a fuel rod passing through the spacer cell and flow diverter. The invention also relates to the combination of a cell flow diverter and vortex generator.
In boiling water nuclear reactors, each fuel bundle comprises an array of fuel rods passing through axially spaced spacers, all encompassed within a fuel channel. The fuel rods comprises full-length fuel rods with one or more part-length fuel rods interspersed at predetermined locations within the array of full-length rods. Part-length fuel rods terminate at an elevation within the fuel bundle typically below one or more of the uppermost spacers of the bundle. As well known, the termination of the part-length fuel rods creates voids in the upper sections of the fuel bundle bounded by adjacent full-length fuel rods. Various swirler vane arrangements have been proposed for disposition on the upper ends of the part-length fuel rods or on the spacers to circulate the boiling water/moderator in the void regions. Certain problems are associated with these prior swirl vane arrangements which include difficulty of fabrication, attachment of the swirl vanes to the spacer, both during initial fabrication and in situ installation and removal of the swirl vane after fuel bundle irradiation. There is therefore a need for a flow diverter for channeling the flow into desired locations and particularly a flow diverter/vortex generator assembly for directing the boiling water/moderator flowing through the spacers and into the voids above part-length rods for flow about and into the interstices of adjacent upper regions of full-length fuel rods.
In accordance with a preferred embodiment of the present invention, there is provided a flow diverter for diverting flow between cells of a spacer for flow within the diverter wherein the diverter channels the flow into a vortex generator for distributing boiling water/moderator onto and into the interstices of adjacent full-length fuel rods adjacent void regions or channel the flow between the cells of the spacer onto a fuel rod passing through the spacer cell mounting the flow diverter. The flow diverter preferably includes a generally cylindrical tube for overlying a cell of a spacer. The flow diverter tube includes a plurality of tabs projecting laterally from the tube generally at perpendicular locations about the axis of the tube. Each tab extends diagonally relative to the rectilinear array of spacer cells into spaces between adjacent cells, i.e., between the rows and columns of cells. For example, each tab extends diagonally into the space between adjacent cells a distance such that the outer edge of the tab extends beyond a straight line interconnecting center lines of diagonally adjacent cells. With the tab occupying the area between the diagonally adjacent cells and being angled laterally outwardly from the diverter in an axial upstream direction, boiling water/moderator is diverted from the interstices of the spacer cells through the tubular diverter for flow in an axial downstream direction at a spacer cell location generally corresponding to the cell location of the diverter. One beneficial effect of this construction and location of the flow diverter is that the coolant flow increases in pressure and velocity as it passes through the flow diverter. This is particularly effective in xe2x80x9csuperchargingxe2x80x9d the flow when the diverter is disposed about a fuel rod.
In a preferred embodiment of the present invention, the flow diverter is employed in conjunction with a vortex generator. In a first form of vortex generator, a cylindrical tube is provided having a plurality of slits opening through a downstream end of the tube. For example, where four vanes are to be provided, eight slits are provided and each vane defined by adjacent slits in the vortex generator tube is twisted such that one edge lies inboard of the circumference of the tube and the opposite edge lies along the circumference of the tube. Tube portions between the slits forming the vanes are removed. The tips of the vanes meet at the central axis of the vortex generator and may be welded to one another at that location. The slit size and shape of the vanes ensure that the vanes of the vortex generator do not extend laterally beyond the periphery of the vortex generator tube.
To secure the vortex generator to the flow diverter, the tube of the flow diverter is preferably provided with a series of circumferentially spaced slots. The base of the vortex generator is provided with spring tabs angled such that upon displacement of the vortex generator toward the flow diverter, e.g., downwardly onto the flow diverter, the spring tabs deflect first inwardly and then outwardly into the slots of the flow diverter to secure the vortex generator to the flow diverter. In another form, the flow diverter and vortex generator may have complementary threads whereby the vortex generator may be screwthreaded onto the flow diverter. The vanes and threads are configured such that the swirling of the flow afforded by the vortex generator is in swirl direction tending to tighten the vortex generator on the flow diverter.
In a further preferred embodiment hereof, the flow diverter comprises a cylindrical tube wherein the tabs are struck from the tube for extension into the interstices between adjacent spacer cells with the vortex generator forming an integral part of the flow diverter tube. The vortex generator is similar to the embodiment first described above without its interconnection with the flow diverter.
In a still further form hereof, the flow diverter may be secured to the spacer, for example, by welding, in a cell location which receives a fuel rod. In this manner, the boiling water/moderator flows from between the spacer cells into the tube of the diverter and into an annular space between the diverter and fuel rod to maintain flow contact with the fuel rod.
In a preferred embodiment according to the present invention, there is provided a flow diverter for diverting flow between cells of a spacer in a nuclear fuel bundle into the diverter and in a downstream flow direction relative to the spacer, the spacer having a rectilinear array of cells, comprising a cylindrical tube for overlying a spacer cell and having an axis, a plurality of tabs projecting laterally from the cylindrical tube at perpendicular locations relative to one another about the axis for disposition in the spacer between diagonally adjacent cells of the rectilinear array thereof, the tabs forming with the axis acute angles for diverting flow through the spacer into the cylindrical tube.
In a further preferred embodiment according to the present invention, there is provided a flow diverter/spacer combination for diverting flow between cells of a spacer in a nuclear fuel bundle for flow within the diverter and in a downstream flow direction relative to the spacer, comprising a spacer having generally cylindrical side-by-side cells in cell positions arranged in parallel rows and parallel columns forming a generally rectilinear array of cells, the cells having parallel axes, a cylindrical tube overlying a cell and having an axis generally coincident with the axis of the cell, a plurality of tabs projecting laterally from the cylindrical tube at perpendicular locations relative to one another about the axis, each tab extending diagonally relative to the rectilinear array of columns and rows of the cells into spaces between diagonally adjacent cells, the tabs forming with the axis acute angles opening in an upstream direction for diverting flow through openings between the cells of the spacer into the cylindrical tube.